This invention relates to chemical lasers and, more particularly, to a system for generating molecular oxygen in the excited singlet-delta electronic state.
Chemical laser systems have proven to be very useful for a number of applications, and considerable interest in their development has evolved. In a chemical laser, the energy required to produce the population inversion necessary for lasing is supplied by chemical reactions. In some cases the lasing species is produced directly by a single chemical reaction. In other cases an excited state of a chemical species is produced chemically and through a combination of chemical reactions and energy transfer a population inversion is produced in another chemical species. An optical laser cavity is then used to produce lasing. For example, in chemical oxygen iodine laser (COIL) systems, basic hydrogen peroxide (BHP) is reacted with a halogen, typically chlorine, to yield electronically excited singlet-delta oxygen, O.sub.2 (.sup.1 .DELTA.). This unstable state of excited oxygen can dissociate molecular iodine and transfer its energy to atomic iodine, the actual lasing species of COIL.
The BHP, which is an unstable solution of aqueous alkaline hydrogen peroxide, is typically generated by reacting an aqueous metal hydroxide, usually potassium hydroxide, with an excess of hydrogen peroxide.
As described in U.S. Pat. No. 5,378,449, the BHP, when reacted with a halogen gas, such as chlorine, produces the excited oxygen, with depletion of the BHP, and generation of salt, such as potassium chloride when the hydroxide is potassium hydroxide and the halogen gas is chlorine.
A typical reaction to form BHP (HO.sub.2.sup.-) is: EQU MOH+H.sub.2 O.sub.2 .fwdarw.M.sup.+ +HO.sub.2.sup.- +H.sub.2 O (1)
where M is an alkali metal from Group IA of the periodic table.
Typical reactions to form the excited oxygen are: EQU X.sub.2 +HO.sub.2.sup.- .fwdarw.O.sub.2 (.sup.1 .DELTA.)+2X.sup.- +H.sup.+( 2) EQU HO.sub.2.sup.- +H.sup.+ .rarw..fwdarw.H.sub.2 O.sub.2 ( 3)
where X is a halogen, typically chlorine.
Unfortunately, after consumption of a small portion of the BHP reactant, a concentrated salt solution can result, with salt precipitation, particularly when the system is operating at low temperatures. The salt is formed from the M.sup.+ from reaction (1) and the X.sup.- from reaction (2), yielding MX. The precipitation of the salt releases heat and removes very substantial fractions of the BHP reactant as a hydrate, possibly as much as 2 or 3 times the pure salt mass. In unfavorable situations, one-third of the BHP may be lost.
For example, in a typical system, 8 moles of H.sub.2 O.sub.2 are combined with 7 moles of potassium hydroxide in a liter of water, and salt formation can occur when as a little as 10% of the BHP is reacted with chlorine.
There are other problems associated with salt formation. The salt is very difficult to quickly remove and its presence can clog feedlines. This is a significant problem when it is desirable to have a closed-loop operation and it is necessary to regenerate the BHP.
Formation of salt can be a significant problem in a particular type of COIL system, which utilizes a transverse uniform droplet oxygen generator (TUDOG), as described in Paper AIAA 94-2454, by Thayer et al., 25th AIAA Plasmadynamics and Lasers Conference, Jun. 20-23, 1994. In the TUDOG system, it is necessary to have high flow rates of the BHP through very small orifices. These orifices can be plugged easily by salt crystals. Further, the salt can also foul in-line heat exchangers.
Accordingly, there is a need for a system for generating molecular oxygen in the excited singlet-delta electronic state which utilizes a high percentage of the BHP that is formed, without any significant insoluble salt formation.